The present disclosure is directed to image registration, and more particularly to a system and method for automatically registering images of different perspectives and images from sensors with different internal geometry.
Military fighter aircraft customers need a capability to target precision guided weapons. These include JDAM guided bombs as well as higher precision weapons that will eventually become available with target strike errors of 10 feet circular error at 50% probability (10 ft. CEP).
Targeting sensors in fighter aircraft, such as forward-looking infrared (FLIR) or synthetic aperture radar (SAR), currently do not provide targeting of sufficient accuracy, even though the sensors provide images of the target area in which the pilot can precisely select a pixel location for the target. This is because sensor pointing controls of sufficient accuracy are not currently employed and are very expensive to implement, and there is insufficient knowledge of the accurate location and orientation of the aircraft. However, the sensor images presented to pilots have sufficient geometric accuracy for precision targeting if means are provided to accurately relate their geometry to ground coordinate systems at a reasonable cost.
By providing a highly precise means to register an accurately geocoded reference image to an on-board sensor image, it is possible to obtain geographic position measurements for targets with an accuracy approaching that of the reference imagery. Such high precision registration must be obtained between images of different perspectives and different internal geometries.
Sensor images do not generally portray target scenes from the same perspective as a given reference image. Reference images may typically be overhead views of the target area, although this is not a requirement. They are also produced by imaging sensors on some type of platform, and may be processed into a special geometry, such as an orthographic projection, which corresponds to a sensor viewing the scene from directly overhead at each point of the scene (a physically unrealizable form of sensor).
On the other hand, sensor images obtained by a fighter aircraft are from a point of view appropriate to the aircraft's operations, including factors such as weapon delivery needs, aircraft safety from enemy defenses, and general flight operations needs. Thus, the sensor image is typically not of the same perspective as a given reference image. Differences range from simple rotation and scale differences, to major differences in obliquity of the view. Such perspective differences make image match particularly difficult.
Sensors of different types also produce images having different internal geometry. This becomes a problem when matching images from lens-based sensors such as FLIR or optical, and synthetic imagers such as SAR. Orthographic references represent another type of synthesized image, with an internal image geometry that cannot directly match any fighter sensor image. Image photomaps or raster digital cartographic maps represent yet another form of possible reference image, but exhibit a cartographic projection, which also is unlike any sensor image geometry.
All of these differences arise from the ways that different sensors in different viewing positions treat the 3-D nature of the scene being viewed, or from the purpose of the display.
The match process of the present disclosure solves the problem of registering images of different perspectives and images from sensors with different internal geometry.